1. Field of the Invention
The present invention relates to a bookbinding system including a back portion forming device that stitches and folds sheet-like recording medium, such as sheets, recording sheets, and transfer sheets (hereinafter, simply referred to “sheets”), on which images are formed, and makes the back portion of a stitched sheet bundle flat; a bookbinding method performed by the bookbinding system; and a bookbinding control program for performing the bookbinding method with a computer.
2. Description of the Related Art
There has been widely known a sheet processing device that is disposed at a rear portion of a main body of an image forming apparatus, and performs post-processing such as stitching on sheets to be output. However, the number of functions of the sheet processing device has been increased in recent years, so that not only side stitching but also saddle stitching are prevalent. Accordingly, a technique, which improves the folding quality of a booklet subjected to saddle stitch and folding, has been proposed as means for improving output quality.
For example, when a sheet bundle is saddle-stitched and center-folded (two-folded), the two-folded sheet bundle is swelled in a thickness direction near the folded portion thereof, which tends to deteriorate the appearance. Further, if the sheet bundle is swelled near the folded portion thereof, the back portion of the booklet becomes thick and an edge thereof becomes thin. Accordingly, when sheet bundles are stacked in the same direction, the stacked sheet bundles are apt to incline as the number of stacked sheet bundles increase. For this reason, if a plurality of sheet bundles is stacked, the inclination increases, so that the stacked sheet bundles collapse. Therefore, it is difficult to stack more than a certain number of sheet bundles. That is, there is a very high demand on the reduction of the folding height (swelling) after bookbinding in the saddle stitching that is widely used in the world as simple bookbinding. In general, several tens bound booklets are generally handled, that is, transported or delivered while being stacked. However, since the bound booklet, which is subjected to saddle stitching as described above, is swelled, only a small number of booklets may be merely stacked.
In contrast, if a booklet is formed by making the folded portion of a two-folded sheet bundle flat in the shape of a spine of a book, swelling of the booklet is pressed. Accordingly, it may be possible to stack a large number of booklets. That is, if only several booklets, which are swelled as described above, are stacked on the table, the stacked booklets collapse, which causes a problem in the handling of the booklets such as storing or transport. However, if a back portion corresponding to the folded portion is made flat, it may be possible to suppress swelling as much as possible and the above-mentioned problem is solved. Meanwhile, the back portion, which is mentioned here, means a back surface section (hereinafter, referred to as a back surface portion) that includes a back cover forming a back surface and front and back cover sections connected to the spine, and corresponds to a portion opposite to the edge of the booklet.
As user's countermeasures, there have been proposed a plurality of additionally folding mechanisms, such as a method of placing and leaving weights on booklets, a mechanism for performing folding several times, a mechanism for performing an additional folding by making a pressurizing roller run on a folded portion, and a mechanism for clamping a front end of a booklet and forming a plane at a folded portion with a back surface pressure roller.
Among these proposed mechanisms, for example, in the invention disclosed in Japanese Patent Application Laid-open No. 2001-260564, front and back surfaces of a booklet, which is formed of a sheet bundle of which a back portion is folded so as to be curved, are gripped and fixed with pressing means so as to be adjacent to a back portion, and a shaping roller presses a protruding back portion with pressure enough to make the curve of the back portion flat and runs on the back portion one time or several times in a longitudinal direction of the back portion, so that the back portion is made flat.
An advantage of making the curve of the back portion flat is obtained in this invention. However, since the back portion is locally and continuously pressed with a pressurizing roller and a plane is formed at the booklet back portion, wrinkles, breakage, or the like might be generated on the back surface or a stitched portion. Further, since the roller is moved along the folded portion, working time is inevitably lengthened.
Further, a sheet bundle forming device, which is disclosed in the invention disclosed in Japanese Patent Application Laid-open No. 2007-237562, includes clamping means, back portion pressing means, and compression means. The clamping means clamps a portion of a folded sheet bundle except for the periphery of the back portion of the folded sheet bundle in a thickness direction. The back portion pressing means presses the back portion in a direction toward an edge, opposite side of the back portion, by pressing a back portion pressing surface against the back portion of the clamped sheet bundle. The back portion pressing surface is formed at a back portion pressing member. The compression means shapes the periphery of the back portion of the sheet bundle by compressing the periphery of the back portion of the pressed sheet bundle in the thickness direction. In the invention of Japanese Patent Application Laid-open No. 2007-237562, portions of the front and back covers near the folded portion, which is pressed in the direction toward the edge with the back portion pressing means to be swelled, are shaped by compression with the compression means; and swelling is suppressed. That is, it may be possible to suppress the influence on the back portion, which is caused by the forming, as compared to the case where a member in the conventional technology is moved along the back portion while being pressed against the back portion with high pressure. Further, a recess is formed on an abutting surface of a sheet back surface abutting means, in order to remove the influence on the high protrusion from the sheet back surface, such as a loop stitcher.
In contrast to the invention disclosed in Japanese Patent Application Laid-open No. 2001-260564, in the invention disclosed in Japanese Patent Application Laid-open No. 2007-237562, it may be possible to form a plane at the booklet back portion without generating serious problems, such as wrinkles or breakage, on the back surface, the stitched portion, or the like. However, in terms of working time, a plurality of means, such as the clamping means, the back portion pressing means, and the compression means, needs to be sequentially operated after the booklet is abutted on the abutting plate and stopped. For this reason, an effect of reducing working time has been insufficient.
Further, in the saddle-stitching and center-folding of a booklet in the conventional technology, a pressurizing force of the folding rollers has been increased for the purpose of reducing the swelling of a booklet or an additionally folding roller has been disposed on the downstream of the folding rollers and an additional folding has been performed, so that the folded portion of the booklet has been pressurized and the swelling of the booklet is reduced. However, in this case, in forming a plane at the back portion of the booklet, the booklet needs to be swelled in the conveying passage. Accordingly, when the reducing the swelling of the folded portion of the booklet has been performed, the booklet is hardly swelled in the forming the plane at the back portion of the booklet, which is disadvantageous in back surface forming.
However, in outputting a booklet that does not need a process of forming the plane at a back portion of a booklet, a pressurizing force of the folding rollers is increased as the present conditions so as to reduce the swelling of the booklet. Alternatively, an additional folding roller and the like are disposed on the downstream of the folding rollers, so that the folded portion of the booklet is pressurized and the swelling of the booklet is reduced. Therefore, the optimum shape of the saddle-stitched and center-folded booklet is varied based on whether a plane is formed or not at the back portion of the booklet.
A problem to be solved by the present invention is: to form an optimum saddle-stitched and center-folded booklet (sheet bundle), respectively, regardless a plane forming process is performed or not at a back portion of a booklet; and to make it capable of forming a plane at a back portion of a booklet.
Meanwhile, in the embodiment to be described below, center folding means corresponds to a folding plate 215 and first folding rollers 230; additionally folding means corresponds to an additionally folding roller 520 or second folding rollers 233; sheet processing device corresponds to a sheet post-processing device 1 and a saddle-stitching device 2; back portion forming device corresponds to reference numeral 3; back surface forming means corresponds to upper and lower assistant clamping plates 320 and 321, upper and lower pressurization clamping plates 325 and 326, an abutting plate 330, and an abutting surface 330a; control means corresponds to CPUs 3-1 and 100-1; conveying means corresponds to upper and lower conveying belts 311 and 312; abutting means corresponds to an abutting plate 330; first clamping means corresponds to upper and lower assistant clamping plates 320 and 321; second clamping means corresponds to upper and lower pressurization clamping plates 325 and 326; sheet ejection means corresponds to a sheet ejection guide plate 335 and upper and lower sheet ejecting rollers 340 and 341; edge cutting means corresponds to an edge cutting device 4; saddle-stitching means corresponds to a saddle-stitching stapler S1; integration means corresponds to a saddle-stitching tray G; and a computer resource corresponds to a CPU, a ROM, and a RAM.